Inflatable tracking antenna



Sept, l, 1964 w. w. BIRD 3,147,478

INFLATABLE TRACKING ANTENNA Filed Aug. 16, 1957 I? 49` 3l 32 l2 /6 \/o 43 44 5s \40 23 f6 4l ffLecroR 58 /QATfR/AL /9 57 /3 In el \42 63,-' 64 65 e2 'J /8 2 Eig-l a Il lo f." l,

l.' l2 3l o G /5 United States Patent O 3,147,478 INFLATABLE TRACKING ANTENNA Walter W. Bird, Williamsville, NY., assignor to the United States of America as represented by the Secretary of the Air Force Filed Aug. 16, 1957, Ser. No. 678,748 4 Claims. (Cl. 343-765) The present invention relates to antennas.

The present invention has more particular relation to the mounting and support of collapsible antennas in such a way as to provide maximum stiffness and minimum distortion of the reflector surface as the antenna is being rotated for tracking operations.

Primary requirements in the construction of antenna assemblies are accuracy of forming, ability to withstand service conditions, such as wind forces and inertia forces due to acceleration or deceleration, and light weight of the antenna components.

In accordance with the present invention, it is proposed to utilize fabricated or similar materials in the construction of the antennas which are lightweight yet collapsible, and to further rigidly support the antenna assembly within an inflatable outer shell, principally by means of pressurization of the outer shell so as to stiffen and stabilize the reflector surface along with the associated antenna components. In this way, the entire assembly is lightweight and can be rolled into a small package for mobility and ease of transportation. Also, the configuration of the reflector surface can be controlled to close tolerances by establishing a pressure differential between opposed sides of the reflector surface, and can further be pressurized to an extent suflicient to overcome inertia forces due to rotation of the asesmbly during tracking operations. Moreover, by using an outer shell of spherical shape, wind resistance is reduced thereby contributing to low power requirements and minimum distortion. Furthermore, the entire assembly can be constructed at low cost, can be rapidly and easily erected, and with the use of proper materials is capable of withstanding frequent erections without adversely affecting the contour of the reflector surface.

Of course, it becomes further necessary to support the antenna and outer shell so that the load of the antenna assembly is uniformly distributed to therefore result in minimum distortion of the antenna, yet permit the desired movement of the antenna. This is accomplished in a novel manner by utilizing a guide frame secured to the outer shell and mounted on a group of rollers or similar slidable surfaces whereby the frame is controlled to pivot and turn the entire assembly. Furthermore the outer shell is secured to the frame in such a Way that the relative position of the two are fixed and when desired the outer shell can be removed then later reinstalled in the same fixed position.

Accordingly, it is an object of the present invention to provide for a lightweight, fabricated reflector surface mounted in a pressurized outer enclosure in such a way as to present a uniform surface in the desired configuration for the distortionless reflection of high frequency electromagnetic wave lengths.

It is an additional object to provide for a lightweight, portable antenna assembly including a collapsible parabolic reflector forming one side of a sealed enclosure with the sealed enclosure mounted and arranged within an outer enclosure in such a way that the reflector surface is rigidly supported against inertial and other exteriorly applied forces during horizontal and vertical rotation.

A further object is to provide for an inflatable antenna mount assembly which is rapidly and easily erectible, is conformable for construction over a wide range of sizes 3,147,478 Patented Sept. 1, 1964 ACC dependent upon the scanning requirements, and which is further capable of withstanding frequent erections without adversely affecting the contour of the reflector surface.

A still further object is to provide for a collapsible antenna assembly support within an inflatable shell which can be mounted for rotation on a rotatable tracking assembly so as to uniformly distribute the weight of, and to dimensionally stabilize, the antenna assembly for the distortionless reflection of high frequency electromagnetic waves.

These and other objects of the present invention will become more apparent from a consideration of the description taken together with the drawing, in which:

FIG. 1 is a side elevational view of a preferred embodiment of an antenna assembly disposed on a tracking assembly for horizontal and vertical scanning;

FIG. 2 is a sectional view of the antenna and tracking assembly taken on lines 2-2 of FIG. 1; and

FIG. 3 is an enlarged fragmentary View showing one means of attachment of the outer shell of the antenna to the tracking assembly, in accordance with the present invention.

With more particular reference to the drawings, there is shown in the preferred embodiment of FIGS. 1 and 2 an antenna mount assembly 10 which is of the mechanical scanning type for use in radar tracking operations. As shown, the antenna mount assembly 10 is broadly comprised of a collapsible antenna 11 supported within an outer shell or enclosure 12, commonly termed a spherodome, and mounted upon a tracking assembly 13 which serves as a means for rotating the antenna and outer shell about both the horizontal and Vertical axes.

In inflated condition, the outer shell 12 is constructed to take the form of a hermetically sealed, spherical enclosure. In that it serves as a principal support means for the antenna 11, it is comprised of a coated fabric of good dimensional stability so as to fully restrain the movement of the antenna; for example, a two-ply, 45 bias material. In the preferred form as shown, the outer spherical enclosure 12 is 32 feet in diameter and is provided with an entrance hatch 14 to permit access into the shell.

The antenna 11 consists of a collapsible, inner enclosure 15 with one side of the enclosure formed to provide a parabolic reflector surface 16 and the complementary side formed as a closing sheet 17 of nonreflective material. An antenna feedhorn 18 is supported on the inner surface of the spherodome 12 in front of and on the central axis of the reflector surface 16 and is positioned by means of suitable guy wires or struts 19 to hold the feedhorn 18 accurately in position with relation to the reflector surface 16. A flexible, fabric or metallic wave guide 20 is connected to the feedhorn 18 and is passed downwardly around the inner surface of the enclosure and out through the lower surface of the spherodome 12 to carry the signal off of the tracking assembly.

It is necessary to mount the reflector surface 16 within the outer enclosure 12 so as to provide and maintain close tolerances on the antenna contour against twisting and shear loads imposed on the outer shell 12. For this purpose, the reflector surface 16 is supported along its peripheral edge against the inner surface of the shell 12 by means of an inflatable support, high pressure tube or structural sectional, collapsible metal ring 21. The closing sheet 17 is preferably constructed to form approximately a mirrored surface of the reflector 16 and is joined to the peripheral edge of the reflector surface 12 so as to provide an inflatable inner enclosure 15 which can also be pressurized. The edges of the reflector surface and closing sheet are then attached to the outer rim of the tube 21 by overlapping the edges and/ or applying a fabric skirt 22 over the edges and bonding the skirt and edges to the tube 21. The skirt 22 is in turn bonded to the inner surface of the spherodome 12 to retain the entire inner enclosure 15 in fixed position with respect to the outer spherodome 12 and to the feedhorn 18.

To maintain a balanced system of loads on the high pressure tube 21 it is preferred to form approximately equal angles of intersection between the edges of the reflector 16 and closing sheet 17 and the tube 21; for example, this may be accomplished by passing a peripheral flap 23 along the inner surface of the tube 21 and connecting the ends of the fiap to the inner surfaces of the closing sheet 17 and refiector 16 adjacent the tube so as t form equal angles of intersection. The flap 23 together with the fabric skirt 22 also assist in maintaining the proper position of the closing sheet 17 and refiector 16 whether in infiated or defiated condition. In the above relation, the tube with the reflector surface and closing sheet normally tend to mutually stabilize one another in the desired fixed position. Under extremely heavy loads, however, it may be necessary to provide cross ties or cables, not shown, which can be extended across the diameter of the high pressure tube in radial fashion in order to retain the shape of the tube in the desired circular configuration.

Both the refiector surface 16 and closing sheet 17 are composed of glass fabric material or other material having a high modulus and good dimensional stability, such as, a vinyl coated Fiberglas. To provide the desired reflective qualities for the reflector surface, a conductive coating is applied to the front surface of the reflector 16, such as, a vapor aluminum coated mylar laminated to the glass fabric. Also, a high modulus material with good dimensional stability is required for the high pressure tube 21; however, due to the flexing to which the tube is subjected, glass fabric has been found to be too brittle and it is preferable to use more iiexible materials, such as, Fortisan rayon. Moreover, either a single-ply or a two-ply, 45 bias construction may be used, although the two-ply construction provides better dimensional stability and greater tear resistance. The fabric skirt 22 and peripheral ap 23 are also made of coated fabric material.

The antenna assembly is infiated to the proper operating position by means of a blower system consisting of an outer spherodome blower apparatus 30 projecting inwardly from the inner surface of the spherodome 12, an antenna blower 31 also projecting inwardly from the inner surface of the spherodome and further projecting through the surface of the reflector 16 to communicate with the inner enclosure, together with a high pressure tube blower having an inlet indicated at 32 in FIG. l of the drawings for inflating the tube 21. It is noted that the specific details of the high pressure tube blower having the inlet 32 is not shown since the specific nature thereof is unimportant to the present invention and, further, the inclusion thereof in either FIGS. l or 2 would tend to obscure other more important details of the invention. Suitable exterior control means (not shown) may be provided to maintain a small pressure differential in the inner enclosure over that maintained in the outer spherodome enclosure 12 so as to stiffen and support the refiector surface 16 in the desired contour; however, the desired pressure differential between the inner enclosure 15 and the outer enclosure 12 may be automatically maintained by the aforesaid antenna blower 31 which blower 31 is preselected as desired to provide the desired pressure differential between the intake opening thereof located in the said outer enclosure 12 and the outlet opening thereof located in the said inner enclosure 15 and thus eliminate any requirement for any exterior control means. The high pressure tube 21 can also be pressurized to the desired pressure level apart from the pressure level in the inner enclosure 15 and outer enclosure 12.

The tracking assembly or guide frame 13 which serves as a mounting base for the antenna assembly is made up of a track support portion 40 which in turn is supported on roller bearings 41 mounted on the rotary stand 42.

The track support portion 40 is formed to uniformly distribute the load of the antenna assembly so as to avoid any tendency to depress the surface and defiect the outer spherical enclosure 12 which might affect the contour of the reflector surface. For this purpose, longitudinal arcuate track members 43 are disposed to extend from the bottom curvature of the spherodome to one side of the spherodome; the tracks 43 are thus curved to conform to the contour of the spherodome surface 12 and are secured in fixed position by means of transverse cross members 44 to the spherodome surface in parallel, spaced relation at right angles to the support tube 21. As shown in FIG. 3, to accurately position and hold the spherodome to the tracks 43, fabric patches 45 are bonded to the surface of the spherodome with the patches being provided with apertures 46 for placement of suitable retaining pins or bolts 47 extending outwardly through the apertures for connection of the tracks 43 to the surface of the spherodome. The bolts 47 extend through bolt receiving holes in the cross members 44 and the bottom surface of the tracks and are secured to the tracks by means of suitable nuts 48. To prevent possibility of tearing of the spherodome surface, reinforced webbing 49 serves as a backing on the inner surface of the spherodome behind the fabric patches 44.

Tilting or rotation of the antenna assembly about the horizontal axes is accomplished in a manner to provide smooth travel of the tracks for scanning between the horizontal and vertical directions. For example, the roller bearings 41 may be positioned on support pins 50 which project laterally from upright standard members 51 extending upwardly at equally spaced intervals from the sides of the rotary stand 42. Four roller bearings 41 are provided with two each disposed to engage the parallel tracks 44 at spaced points and with the ends of the bearings enclosed by stationary retainer plates 52. The retainer plates 52 have an inwardly curved lip 52a at their upper extremities to engage the under surface of the tracks 43 so as to retain the tracks in position against the roller bearings 41 and thus prevent accidental separation between the tracks and rollers. The four standards 51, as shown in FIGS. 1 and 2, are braced in pairs by means of cross pins 53 to maintain the proper alignment between the corresponding pairs of rollers; however, the standards are not braced transversely to the tracks in order that a certain amount of flexibility is permitted to allow the rollers to follow the tracks more easily. To drive the tracks on the rollers 41 a power winch 56 is mounted on the rotary stand 42 and is driven by a motor 57 through gearing 58 to wind and unwind a cable 59 which is wrapped around the winch and attached at its opposed ends to the opposite, extreme cross members 45 at each end of the tracks.

The rotary stand 42 which carries the roller assembly also includes a horizontal turntable 60 which is free to rotate by supporting the turntable on frusto-conical roller bearings 61 which in turn are mounted on a platform as represented at 62. Rotation of the entire antenna mount assembly 10 about a vertical axis is suitably accomplished by providing the horizontal turntable 60 with a circular rack 63 joined to the under surface of the turntable 60 for engagement by a pinion gear 64 which is in turn driven by motor 65. Thus the rack and gear arrangement on the turntable serve to rotate the entire base structure along with the antenna assembly about the vertical axis, and the power winch 56 operates to tilt the antenna assembly about the horizontal axis.

By accurately controlling the pressure differential between the inner enclosure and the spherodome, and by pressurizing the spherodome to provide a tension surface supporting the inner shell in fixed position, it is thereby possible to insure substantially distortionless reflection of high frequency Wave lengths with the use of an antenna system constructed of collapsible, fabricated materials and housed within a radome. Furthermore, by providing a broad base for supporting the antenna assembly during tracking operations effects of the wind and inertia forces are greatly reduced and substantially eliminated. Of course, it is to be understood that other types of base support structures could be used in place of the track assembly 13 as described for mounting and support of the antenna assembly for scanning or tracking operations, although the tracking assembly, as described, has been found to be particularly effective.

Having thus described a preferred embodiment of the present invention, it is to be understood that various modifications may be made without departing from the scope of the present invention as defined by the appended claims.

I claim:

1. In an antenna mount assembly, the combination of an outer enclosure; an inner inflatable enclosure defined by a collapsible parabolic reflector surface incorporating an overlapping peripheral edge, complementary flexible means having an adjacently positioned edge in overlapping relation to the overlapping peripheral edge of said reflector surface and joined to the peripheral edge of said reflector to close the front of said reflector into a sealed, inner enclosure, means supporting the peripheral edge of said inner enclosure against the inner surface of said outer enclosure comprising an inflatable support, high pressure tube circumferentially disposed within said inner enclosure in stiff supporting contact along said peripheral edge when in inflated condition, fabric support means bonded over said tube and the overlapped, adjacently positioned edges of said reflector surface and complementary means and to the inner surface of said outer enclosure for joining said reflector surface and said complementary means to each other and to said tube and to fix said inner enclosure to said outer enclosure; and individual blower means communicating with said inner enclosure and outer enclosure to inflate and pressurize the same to establish a predetermined pressure differential between said inner and outer enclosures operating to stiffen and support said reflector surface, together with means adapted to pressurize said support tube to a substantially rigid, circular configuration against the inner surface of said outer enclosure, and additional support means for insuring the proper positioning of said tube relative to said inner enclosure comprising a continuous fabric flap peripherally disposed along the inner surface of said tube and terminating in end portions joined to the inner surfaces of said reflector surface and said complementary means adjacent said ltube to thereby form substantially equal angles of intersection between the edges of said reflector surface and said complementary means and said tube.

2. A mechanical scanner apparatus adaptable for rotation in azimuth and elevation, comprising an outer inflatable enclosure, a collapsible antenna assembly mounted within said outer enclosure comprising a reflector surface forming one side thereof and a non-reflective, complementary surface forming the other side thereof, each of said reflector and nonreflective surfaces having an overlapped, peripherally joined end, and circumferentially disposed fabric support means afllxing said reflector and nonreflective surfaces to each other, said fabric support means comprising a fabric skirt positioned between said inner and outer enclosures and bonded to the overlapped, peripherally joined ends of said reflector and nonreflective surfaces and the inner surface of said outer enclosure, and a tracking assembly including roller-bearing supported track members conforming to the contour of a segment of the exterior surface of said outer enclosure in inflated condition and extending from the bottommost curvature of said outer enclosure to one side thereof, transversely extending connection means for rigidly securing said track members in spaced parallel relation to the exterior surface of said outer enclosure comprising fabric bond means affixed to the outer surface of said outer enclosure and having apertures incorporated therein for rigid connection to said track members, a plurality of spaced, parallel cross brace members rigidly secured between said fabric bond means and said track members, and reinforcing Webbing means aflixed to the inner surface of said outer enclosure opposite said fabric bond means, and a rotary stand including a horizontal turntable and a group of spaced roller members carried by said turntable for engaging and supporting said tracks on said turntable for longitudinal movement, and drive means connected to said tracking assembly for movement of said tracks on said rollers in elevation and for rotation of said turntable azimuth, said track members being of a length and parallel spacing sufficient to uniformly distribute the load of said outer enclosure on said tracking assembly and to permit elevational scanning by said antenna between the horizontal and vertical directions.

3. A mechanical scanner apparatus for rotation in azimuth and elevation, comprising an outer inflatable enclosure of spherical shape, an inner inflatable, pressurized enclosure comprising an antenna including a collapsible, parabolic reflector surface and a nonreflective parabolic surface in closing, air-tight relation thereto with each having a peripheral end portion proportioned for attachment tothe inner circumference of said outer enclosure, means supporting the peripheral end portions of said inner enclosure against the inner surface of said outer enclosure comprising a reinforcing, high-pressure flexible, peripherally disposed support ring member supporting said inner inflatable enclosure against said outer enclosure, additional support means including fabric skirt means joining the peripheral end portions of said reflector and nonreflective surfaces to each other and to said support ring member and the inner surface of said outer enclosure, and a tracking assembly including a pair of arcuate track members conforming to the contour of a circular segment of said outer enclosure in inflated condition, connection means for securing said tracks in spaced parallel relation to the exterior surface of said outer enclosure and in such a way as to provide for tilting of said reflector surface between the horizontal and vertical directions, and a rotary stand including a horizontal turntable and a group of roller members carried by said turntable to engage said tracks including means to maintain said tracks in contact with said rollers, and drive means connected to said tracking assembly for rotation of said scanner in azimuth and elevation, said tracks being so constructed and arranged in relation to said outer enclosure and said reflector as to uniformly distribute the load of said outer enclosure over the length of said tracks and Ito prevent distortion of said reflector surface as said scanner is rotated in azimuth and elevation.

4. A collapsible, inflatable mechanical scanner apparatus for rotation in azimuth and elevation, comprising an outer inflatable enclosure of substantially spherical shape, an inner, sealed enclosure comprising a collapsible antenna having a flexible parabolic reflector surface having an overlapped edge and defining one side and a nonreflective closure sheet having an overlapped edge in overlapping relation to the overlapped edge of said reflector surface and defining the opposed side of said inner sealed enclosure in air-tight relation thereto, said sealed enclosure disposed within said outer enclosure, means supporting the peripheral edge of said inner enclosure against the inner surface of said outer enclosure comprising an inflatable support tube disposed in peripheral relation within said inner enclosure in semi-rigid contact along the junction between said reflector and said closure sheet, and semi-rigid, circularly disposed fabric attachment means mounted in peripheral, bonded relation to the overlapped edges of said reflector surface and said closure sheet to support the latter in contacting relation against the outer rim of said tube and the inner surface of said outer enclosure providing additional support between said support tube and the peripheries of said inner and outer enclosures, blower means communicating with and pressurizing said inner and outer enclosures to establish a predetermined pressure differential between said inner and outer enclosures to provide for stilening of said reector surface Within said outer enclosure together with means adapted to pressurize said support tube [to a substantially rigid circular configuration so as to restrain the movement of said reector surface with respect to said outer enclosure, and a tracking assembly including a pair of circular track members being of a length sufficient to extend from the bottom exterior surface of said outer enclosure to a side thereof, fabric connection means attached to the exterior surface of said outer enclosure for securing said track members to the exterior surface of said outer enclosure in spaced parallel relationA and at right angles to said support tube, and a rotary stand including a horizontal turntable and a group of upright roller bearing members carried by said turntable for engaging and supporting said track members at spaced intervals on said turntable, a plurality of roller bearings supported on said bearing members, retained plate means enclosing said bearings each having an inwardly curved lip in engagement with said track members and drive means connected to said tracking assembly for movement of said track members with respect to said rollers and for rotation of said antenna upon said horizontal turntable, said track members being operative to distribute the load of said outer enclosure over the length of said track members and to prevent distortion of said antenna as said scanner is being rotated in azimuth and elevation.

References Cited in the le of this patent UNITED STATES PATENTS 2,415,407 Benioi Feb. 11, 1947 2,460,274 Benioif Feb. 1, 1949 2,534,716 Hudspeth Dec. 19, 1950 2,654,031 Mullins Sept. 29, 1953 2,814,038 Miller Nov. 19, 1957 2,913,726 Currie et al Nov. 17, 1959 

2. A MECHANICAL SCANNER APPARATUS ADAPTABLE FOR ROTATION IZIMUTH AND ELEVATION, COMPRISING AN OUTER INFLATABLE ENCLOSURE, A COLLAPSIBLE ANTENNA ASSEMBLY MOUNTED WITHIN SAID OUTER ENCLOSURE COMPRISING A REFLECTOR SURFACE FORMING ONE SIDE THEREOF AND A NON-REFLECTIVE, COMPLEMENTARY SURFACE FORMING THE OTHER SIDE THEREOF, EACH OF SAID REFLECTOR AND NONREFLECTIVE SURFACES HAVING AN OVERLAPPED, PERIPHERALLY JOINED END, AND CIRCUMFERENTIALLY DISPOSED FABRIC SUPPORT MEANS AFFIXING SAID REFLECTOR AND NONREFLECTIVE SURFACES TO EACH OTHER, SAID FABRIC SUPPORT MEANS COMPRISING A FABRIC SKIRT POSITIONED BETWEEN SAID INNER AND OUTER ENCLOSURES AND BONDED TO THE OVERLAPPED PERIPHERALLY JOINED ENDS OF SAID REFLECTOR AND NONREFLECTIVE SURFACES AND THE INNER SURFACE OF SAID OUTER ENCLOSURE, AND A TRACKING ASSEMBLY INCLUDING ROLLER-BEARING SUPPORTED TRACK MEMBERS CONFORMING TO THE CONTOUR OF A SEGMENT OF THE EXTERIOR SURFACE OF SAID OUTER ENCLOSURE IN INFLATED CONDITION AND EXTENDING FROM THE BOTTOMMOST CURVATURE OF SAID OUTER ENCLOSURE TO ONE SIDE THEREOF, TRANSVERSELY EXTENDING CONNECTION MEANS FOR RIGIDLY SECURING SAID TRACK MEMBERS IN SPACED PARALLEL RELATION TO THE EXTERIOR SURFACE OF SAID OUTER ENCLOSURE COMPRISING FABRIC BOND MEANS AFFIXED TO THE OUTER SURFACE OF SAID OUTER ENCLOSURE AND HAVING APERTURE INCORPORATED THEREIN FOR RIGID CONNECTION TO SAID TRACK MEMBERS, A PLURALITY OF SPACED, PARAL- 